Vantaggi
Not a bad place to start out if you lack discipline or direction and especially if you're young and don't have any inkling what you want to do. Especially with the new GI Bill, you get a couple years in, and then you can go get a bachelors degree after maturing to the point of knowing what you want to do. If you show initiative, you have the opportunity to take on responsibility at an early age that you might not get in the private sector for 10-20 years in a job. When deployed, you have the opportunity to bank some money that might otherwise be spent while in the states. Some of the individuals you work with you will be amazed at their dedication to the Army and the missions at hand.
Svantaggi
I liken the US Army to working at the Post Office with Guns. Extremely bureaucratic. Inefficient. A lot of idiots in charge. Having to move every 2-4 years. Career progression possibly limited by inept bureaucrats. For officers- your pay "stagnates" (in comparison to private sector positions) at upper levels. Wartime hazards: getting shot at, pressure deployments causes on marriage, the fact that a contractor is getting paid 4-10 times what you are earning. A beautiful metaphor for career progression to becoming a general: it's a single mistake marathon - make one mistake (not having a Ranger tab, taking risks) and you are out of the running for the higher ranks (Colonel and higher)